This invention pertains to the art of manufacturing extruded articles from extrudable material such as ceramic batches and similar materials which have the property of being able to flow or plastically deform during extrusion, while being able to become sufficiently rigid immediately thereafter so as to maintain their structural integrity. More particularly, the present invention relates to an improved extrusion die mask utilized in conjunction with an existing extrusion die, for not only providing such extrusion die with greater versatility, but also for improving skin characteristics about cellular or honeycomb articles which may be extruded by such die. The extrusion die may be virtually any known construction, however the extrusion die mask of the present invention has particular application with respect to extrusion dies having multiple core pins for forming cellular or honeycomb structures, such as disclosed in U.S. Pat. No. 3,790,654. That is, such extrusion dies for making honeycomb structures necessitate the formation of numerous core pins, and accordingly the manufacture of such dies is not only very complex but very costly. Further, every time a honeycomb structure having a new size or shape is required, it necessitates the burdensome manufacture of an additional new costly die. Not only does this require the maintenance of a relatively large inventory of extrusion dies with different sizes and configurations, but also many of such dies become obsolete as size and shape requirements are varied.
U.S. Pat. No. 3,836,302 discloses a mask or face plate for overlying a portion of a discharge face of an extrusion die so as to provide such die with greater flexibility and variability. The mask of said invention did in fact function satisfactorily to provide extrusion dies with greater flexibility and variability, and when such mask was utilized with dies for forming honeycomb structures, it also provided an integral skin or casing about such structures. However, during the formation of the skin about the honeycomb structures, the mask had a tendency to crush peripheral cells as the structure passed through the central opening of the mask. Further, the surface of the skin produced by such mask had a tendency to be fairly rough, and was not of a character to provide a high degree of isostatic crushing strength.
An improved extrusion die mask is disclosed in copending patent application Ser. No. 532,362, now U.S. Pat. No. 3,947,214 assigned to the assignee of this application, and includes a recessed reservoir and a flow control or metering gap in its inlet face for forming a substantially smooth integral skin about a honeycomb article without causing peripheral cell distortion and with improved isostatic crushing strengths.
The present invention has not only overcome the problems of rough skin texture and peripheral cell distortion which were encountered with the prior art devices, but also provides a more easily manufacturable extrusion die mask which results in better product selection than that obtainable with the mask of said copending application.